Start recordings at the first accepted video frame

electron/native/ScreenCaptureKitRecorder.swift

@@ -394,13 +394,8 @@ final class ScreenCaptureRecorder: NSObject, SCStreamOutput, SCStreamDelegate {
 
 	func stream(_ stream: SCStream, didOutputSampleBuffer sampleBuffer: CMSampleBuffer, of outputType: SCStreamOutputType) {
 		guard sessionStarted, sampleBuffer.isValid, isRecording else { return }
-		guard let presentationTime = adjustedPresentationTime(for: sampleBuffer, outputType: outputType) else { return }
 
 		if outputType == .screen {
-			if frameCount > 0 && CMTimeCompare(presentationTime, lastVideoPresentationTime) <= 0 {
-				return
-			}
-
 			guard let attachments = CMSampleBufferGetSampleAttachmentsArray(sampleBuffer, createIfNecessary: false) as? [[SCStreamFrameInfo: Any]],
 					  let attachment = attachments.first,
 					  let statusRawValue = attachment[SCStreamFrameInfo.status] as? Int,
@@ -413,8 +408,10 @@ final class ScreenCaptureRecorder: NSObject, SCStreamOutput, SCStreamDelegate {
 				  assetWriter?.status == .writing,
 				  videoInput.isReadyForMoreMediaData else { return }
 
-			if firstSampleTime == .zero {
-				firstSampleTime = sampleBuffer.presentationTimeStamp
+			// Only a complete frame that the writer can accept may establish time zero.
+			guard let presentationTime = adjustedPresentationTime(for: sampleBuffer, outputType: outputType) else { return }
+			if frameCount > 0 && CMTimeCompare(presentationTime, lastVideoPresentationTime) <= 0 {
+				return
 			}
 
 			lastSampleBuffer = sampleBuffer
@@ -439,10 +436,16 @@ final class ScreenCaptureRecorder: NSObject, SCStreamOutput, SCStreamDelegate {
 						print("Recording started")
 						fflush(stdout)
 					}
+			} else if frameCount == 0 {
+				// A failed crop/append must not leave an empty interval before frame one.
+				firstSampleTime = .zero
 			}
 			return
 		}
 
+		guard frameCount > 0,
+			  let presentationTime = adjustedPresentationTime(for: sampleBuffer, outputType: outputType) else { return }
+
 		if outputType == .audio {
 			guard let systemAudioInput else { return }
 			appendAudioSampleBuffer(sampleBuffer, to: systemAudioInput, of: systemAudioWriter, firstSampleTime: &firstSystemAudioSampleTime, lastPresentationTime: &lastSystemAudioPresentationTime, presentationTime: presentationTime)

electron/native/ScreenCaptureKitRecorder.test.ts

@@ -84,3 +84,19 @@ describe("ScreenCaptureKitRecorder window capture", () => {
 		expect(recorderSource).toContain("self.windowCropRect = cropRect");
 	});
 });
+
+
+describe("ScreenCaptureKitRecorder first frame timing", () => {
+	const callback = recorderSource.slice(recorderSource.indexOf("func stream(_ stream:"), recorderSource.indexOf("func stream(_ stream:") + 5000);
+	it("validates a complete frame and writer readiness before setting time zero", () => {
+		const clock = callback.indexOf("adjustedPresentationTime(for:");
+		expect(clock).toBeGreaterThan(callback.indexOf("status == .complete"));
+		expect(clock).toBeGreaterThan(callback.indexOf("videoInput.isReadyForMoreMediaData"));
+	});
+	it("resets the origin after a rejected first frame and gates audio on accepted video", () => {
+		expect(callback).toMatch(/else if frameCount == 0\s*\{[^}]*firstSampleTime = \.zero/);
+		const audioGuard = callback.indexOf("guard frameCount > 0,");
+		expect(audioGuard).toBeGreaterThan(0);
+		expect(audioGuard).toBeLessThan(callback.indexOf("if outputType == .audio"));
+	});
+});